Method and apparatus for hardening a surface of a component

ABSTRACT

A method and apparatus for surface hardening parts is disclosed. To harden a surface of a part, a relative movement, or advancing motion, is established between the part and at least one sonotrode-like tool which is excited in the ultrasonic frequency range. The tool is aligned during the surface hardening in such a way to the surface of the part to be hardened that a tool axis running in the effective direction of the tool runs at an angle to the surface of the part to be hardened.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of International Application No. PCT/DE2005/002115, filed Nov. 24, 2005, and German Patent Document No. 10 2004 058 146.0, filed Dec. 2, 2004, the disclosures of which are expressly incorporated by reference herein.

The invention relates to a method for surface hardening parts. The invention further relates to a device for surface hardening parts.

Gas turbine components, for example parts of aircraft engines, are subject to high loads in operation which can result in wear and a failure of the parts. Since, for example, aircraft engines must satisfy stringent requirements with respect to reliability, weight, power, economy and service life, every potential for optimization must be exploited. This includes optimized utilization of the potential of materials from which the parts are produced. Special importance attaches to the surfaces of the parts since the surfaces, or edge layers, are exposed to maximum load in operation. So the surfaces, or edge layers, mostly form the starting point when a part fails. For the optimized exploitation of the material's potential and to extend the service life of parts, it is already known from the prior art to harden the parts on their surfaces or edge layers. By hardening the surface of the parts, the service life of the part can therefore be extended.

In the prior art the surface hardening of parts is preferably carried out by shot peening. In shot peening, balls are accelerated using compressed air, by means of a spinner gate or also with the aid of a sonotrode vibrating in the ultrasonic frequency range and aimed at a surface of a part to be hardened. The shot accelerated, for example, with the help of the sonotrode strikes the surface of the part to be hardened in the sense of statistical distribution and achieves in this way a consistent hardening at the surface of the part to be hardened. The energy provided by a sonotrode is thus transmitted in shot peening indirectly through the shot onto the surface to be hardened of the part being shot peened.

It is further known in practice to harden a part in the area of a surface of the part by moving a sonotrode-like tool in the sense of an advancing motion relative to the part whereby the sonotrode-like tool directly or immediately hardens the surface of the part in the sense of a hammer-like movement. The tool is aligned to the part in such a way that a tool axis running in the effective direction of the particular tool runs perpendicular to the surface to be hardened.

Starting from this point, the problem of the present invention is to create a novel method for surface hardening of parts and a suitable device.

This problem is solved by a method for surface hardening parts. In accordance with the invention, the or each sonotrode-like tool is aligned during surface hardening in such a way with the surface of the part to be hardened that a tool axis running in the effective direction of the particular tool runs at an angle to the surface of the part to be hardened.

Within the meaning of the present invention it is provided to align the or each sontrode-like tool which can be excited in the ultrasonic frequency range during surface hardening in such a way that the tool axis of the particular tool runs at an angle to the surface to be hardened. As the result of this angled position of the sonotrode-like tool to the surface to be hardened and depending on the direction of movement of the relative movement between the part and the tool, selected, draw-oriented hardening conditions can be achieved in the surface of the part to be hardened. The invention permits a rapid, reproducible, reliable and economical surface hardening of parts on flat and curved surfaces of the parts, including the treatment of highly stressed surface areas, such as holes, edges or weld seams even on thin-walled parts. The sonotrode-like tool which can be excited in the ultrasonic frequency range preferably has a contour, or geometry matching the surface to be hardened.

The selected, draw-oriented hardening of the surface of the part can be carried out both along the surface of the part and also in a downward direction. Through the suitable choice of process parameters, it is possible to achieve high thermal and mechanical stability for the hardening conditions. With the aid of the method in accordance with the invention, the static and dynamic strength of the parts can be increased. It is also possible to create nanocrystalline edge layer structures which, among other things, optimize the wear properties and corrosion characteristics. Furthermore, through selectively introduced, draw-oriented hardening conditions, the vibration characteristics of thin-walled parts in particular can be optimized in the resonance frequency range. Using the method in accordance with the invention for surface hardening, the surface roughness of a part can also be reduced or the surface can be given a special microprofiling to achieve fluidic optimization of the parts.

In accordance with an advantageous refinement of the invention, during surface hardening a tool head facing the part is pressed with a contact force against the surface of the part to be hardened.

Preferably during surface hardening the tool axis of the particular tool and the surface of the part in the section in which the tool head is pressed against the surface to be hardened include an angle between 10° and 80°, where the contact force of the tool head against the surface of the part to be hardened lies between 10 N and 100 N and where the introduction of force takes place with a frequency between 15 kHz and 50 kHz.

The device in accordance with the invention for surface hardening of parts is further described below.

Preferred refinements of the invention can be found in the description hereinafter. Embodiments of the invention, without being restricted thereto, are explained in more detail using the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a highly schematized representation to clarify the method in accordance with the invention for surface hardening of parts; and

FIG. 2 shows a highly schematized representation of a device in accordance with the invention for surface hardening of parts.

DETAILED DESCRIPTION OF THE DRAWINGS

In what follows the present invention is described in greater detail with reference to FIGS. 1 and 2.

FIG. 1 shows a schematized view of a part 10, where the part is undergoing surface hardening on one surface 11 within the meaning of the present invention. To surface harden the part 10 on the surface 11, a sonotrode-like tool 12 is used, where to surface harden the part 10 a relative movement, or an advancing motion, between the part 10 and the tool 12 is established. Preferably the part to be processed 10 stands still and the tool 12 is moved relative to the motionless part 10. FIG. 1 visualizes the relative movement, or the advancing motion, between the fixed part 10 and the moving tool 12 with an arrow 13.

The sonotrode-like tool 12 can be excited in the ultrasonic frequency range and transfers the energy to harden the surface 11 of the part 10 directly onto the surface 11 of the part 10. The tool 12 comprises a sonotrode 14 with a sonotrode head 15 acting on the surface to be hardened 11, where the excitation of the sonotrode 14 takes place through a piezoceramic actuator 16. The actuator 16 sets the sonotrode 14 vibrating, where the sonotrode head 15 transfers the vibrational energy to harden the part 10 to the surface 11 of the part. The effective direction of the sonotrode 14, or of the tool 12, is visualized in FIG. 1 by a double-headed arrow 17.

Within the meaning of the present invention, it is now provided to align the tool 12 during the surface hardening of the part 10 in such a way with the surface 11 of the part 10 to be hardened that a tool axis 18 running in, or parallel to, the effective direction (arrow 17) of the tool 12 runs at an angle to the surface 11 of the part 10 to be hardened or at an angle to the direction (arrow 13) of the relative movement or advancing movement between the part 10 and the tool 12. In the surface hardening, the tool axis 18 of the tool 12 and the surface 11 of the part 10 include an angle between 10° and 80°, preferably an angle between 30° and 60°. During the treatment of the entire surface 11, this angle between the tool axis 18 and the surface 11 of the part 10 is preferably kept constant. If there is a part with a curved surface, the tool 12 must be permanently adjusted as needed to match the contour of the surface to be hardened.

It is also possible to treat the surface 11 of the part 10 in different sections in such a way that the surface hardening is performed in the different sections with different angles between the axis of the tool 18 and the surface 11 of the part 10. Furthermore, the direction of movement of the relative movement, or advancing movement, between the tool 12 and the part 10 can be changed. As a result it is possible to achieve different states of hardening of the surface 11 of the part 10 in different sections.

Within the meaning of the present invention, during surface hardening of the part 10 the tool head of the tool, or sonotrode head 15 of the sonotrode facing the part 10 is pressed with a contact force against the surface 11 of the part 10 to be hardened. The contact force of the tool 12 against the surface 11 of the part 10 is of a magnitude between 10 N and 100 N. During surface hardening, the tool 12 is excited with a frequency between 15 kHz and 50 kHz to introduce force. Preferably the frequency to excite the tool is 20 kHz. With such a high frequency for the introduction of force in surface hardening, even thin-walled parts represent such a great inertial mass that good surface hardening can be performed with low contact forces without changing the geometry of the parts unacceptably. For example, thin vanes of gas turbine blades can be hardened with great precision.

In the surface hardening, the relative movement between the part 10 and the tool 12 preferably takes place with an advancing speed that is between 1 mm/s and 1,000 mm/s. The mass of the sonotrode which acts directly through the sonotrode head 15 on the surface 11 of the part 10 to be hardened is preferably of a magnitude between 0.1 kg and 1 kg.

Within the meaning of the method in accordance with the invention, the surface hardening of a part is performed by pressing a sonotrode-like tool with a specific contact force against a surface of a part to be hardened such that a tool axis of the tool runs at an angle to a surface of the part and at an angle to a direction of movement of the tool. As a result, draw-oriented hardening conditions can be selectively created in the surface of the part to be hardened.

To minimize wear on the tool head, or sonotrode head 15 when surface hardening the part 10, the tool head is armored. This can be achieved by the use of high-strength inserts, for example of wolfram-carbide, or by coating the tool head 15 with titanium-nitride for example. Depending on the desired hardening conditions within the surface to be hardened 11, the tool head has a punctiform or linear or planar shape.

The sonotrode-like tool 12, or the sonotrode head 15, which can be excited in the ultrasonic frequency range preferably has a geometry matched to the surface to be hardened.

In the surface hardening of the part 10 on the surface of the part, the tool 12, or the sonotrode 14, can rotate about the tool axis 18. This rotary motion is visualized by the arrow 19 in FIG. 1. The rotation of the tool 12 about the tool axis 18 in surface hardening of the part 10 has the advantage that the contact point 20 between the tool head 15 and the surface 11 of the part 10 changes continuously. As a result, the tool head 15 is subject to more even wear than in the case of a non-rotating tool 12.

In the surface hardening, an electrical voltage can be applied between the tool 12 and the part 10. As a result, heating of the part 10 is possible in the surface hardening at the contact point 20 whereby the hardening effect can be optimized.

Within the meaning of the present invention, as already mentioned, a part can be hardened in different sections of its surface to be hardened with different angled positions of the tool with respect to the part. Furthermore, the direction of the relative movement between the part and the tool can be adjusted. Through multiple surface hardening, crossing as required with different angled positions between the tool and the part, precisely adjusted hardening conditions can be created in the part. Furthermore, the hardening of the part can be performed with several sonotrode-like, preferably phase-controlled tools.

To provide for the relative mobility of the tool 12 with respect to the part 10 to be hardened on its surface 11, the tool 12 is carried in accordance with FIG. 2 on a motion manipulator 21, preferably on a robot. With the assistance of the motion manipulator 21, the tool 12, or the tool head 15, can move anywhere in space and be aligned anywhere to the surface 11 of the part 10 to be hardened. In the embodiment from FIG. 2, a line generator system 22 is assigned to the tool 12 with the help of which the effective direction of the tool 12 can be rendered visible on the surface 11 of the part 10. The alignment of this effective direction to a contact point on the surface 11 of the part 10 can be implemented, for example, by a camera system 23. If an extremely precise angular alignment of the effective direction is required, this can be done by means of a special angle measuring system with a rotatable autocollimation telescope and a rotatable mirror.

In the surface hardening, vibration forms of the particular tool 12 can be used whose effective direction does not run parallel to the excitation direction of the particular tool. These are flexural vibrations of the sonotrode.

Using the method in accordance with the invention and the device in accordance with the invention, locally limited, defined, draw-oriented hardening conditions can be introduced into a surface of a part to be hardened. The hardening conditions can be adapted to the geometry and primary load direction of the part. Defined hardening patterns can be realized on the surface of a part. With the aid of the method in accordance with the invention, the vibration resistance and life of the part can be increased. This applies both to the LCF (low cycle fatigue) life and to the HCF (high cycle fatigue) life of the part. 

1-18. (canceled)
 19. A method for surface hardening of parts, specifically of gas turbine parts, wherein to harden a surface of a part a relative movement, or advancing motion, between the part and a sonotrode-like tool which is excited in an ultrasonic frequency range is established, wherein the tool in the surface hardening is aligned in such a way to the surface of the part to be hardened that a tool axis running in an effective direction of the tool runs at an angle to the surface of the part to be hardened.
 20. The method according to claim 19, wherein the tool axis running in the effective direction of the tool runs at the angle to the surface of the part to be hardened and at an angle to a direction of the advancing motion between the part and the tool.
 21. The method according to claim 19, wherein during the surface hardening, the tool axis of the tool and the surface of the part, in a section in which a tool head is pressed onto the surface to be hardened, include an angle between 10° and 80°.
 22. The method according to claim 21, wherein the angle is between 30° and 60°.
 23. The method according to claim 19, wherein during the surface hardening a tool head of the tool facing the part is pressed against the surface of the part to be hardened with a contact force.
 24. The method according to claim 23, wherein the contact force is between 10 N and 100 N.
 25. The method according to claim 19, wherein during the surface hardening a force is introduced through the tool with a frequency of 15 kHz to 50 kHz.
 26. The method according to claim 19, wherein during the surface hardening the relative movement between the part and the tool takes place with an advancing speed between 1 mm/s and 1,000 mm/s.
 27. The method according to claim 19, wherein during the surface hardening the part remains still and the tool is moved relative to the part in such a way that during an entire surface hardening process the angle between the tool axis and the surface to be hardened is approximately constant.
 28. The method according to claim 19, wherein during the surface hardening the tool is rotated about the tool axis.
 29. The method according to claim 19, wherein during the surface hardening vibrational forms of the tool are used whose effective direction does not run parallel to a direction of excitation of the tool.
 30. The method according to claim 19, wherein during the surface hardening an electrical voltage is applied between the part and the tool.
 31. The method according to claim 19, wherein the surface of the part to be hardened is treated several times by the tool, specifically with different angles between the tool axis and the surface to be hardened and/or with different directions of movement between tool and the part.
 32. A device for surface hardening parts, specifically to perform the method according to claim 19, having the sonotrode-like tool excitable in the ultrasonic frequency range, wherein a tool head with which the tool is pressable against the surface of the part to be hardened, has a punctiform or linear or plane shape.
 33. The device according to claim 32, wherein the tool head is armored, specifically by coating the tool head with titanium nitride.
 34. The device according to claim 32, wherein the tool head of the tool is pressable with a contact force between 10 N and 100 N against the surface of the part to be hardened.
 35. The device according to claim 32, wherein the tool is excitable with a frequency of 15 kHz to 50 kHz.
 36. The device according to claim 32, wherein the tool is moveable at an advancing speed between 1 mm/s and 1,000 mm/s relative to the surface of the part to be hardened.
 37. A method for hardening a surface of a component of a gas turbine, comprising the steps of: relatively moving a sonotrode-like tool with respect to the component; exciting the tool in an ultrasonic frequency range; and aligning the tool with respect to the surface of the component such that a tool axis running in an effective direction of the tool is disposed at an angle to the surface.
 38. An apparatus for hardening a surface of a component of a gas turbine, comprising: a sonotrode-like tool, wherein the tool is excitable in an ultrasonic frequency range; and a motion manipulator, wherein the tool is carried on the motion manipulator such that the tool is relatively moveable with respect to the component and is alignable with respect to the surface of the component such that a tool axis running in an effective direction of the tool is disposed at an angle to the surface. 